A pearl of wisdom from Wilwood’s Michael Hamrick: “When I’m asking about what someone wants out of a brake system, I need to know how the chassis, suspension and tires are all working together.”
The role tires play is particularly important: No matter how good your brakes are, it’s ultimately those four contact patches and their interface with the pavement that …
So to slow that car for the corner, we have to shed 0.285kWh of kinetic energy–about 15 minutes of the power needed to keep our house cool and tunes cranked–and turn it into something else. Remember that energy can’t be created or destroyed; it can only be turned into some other type of energy.
We could turn it into sound or light, but those are fairly efficient forms of energy, so we’d have to produce a lot of them in a short time to reduce speed enough to make this corner. We certainly don’t want to blind or deafen everyone within the entire ZIP code.
So we need to convert that kinetic energy into something more manageable for this situation. How about heat? Brakes do that by using friction.
Tires really can affect braking performance. We collected these two data traces during a recent tire test, and both show the same car braking in the same corner–but on different tires. The additional grip of the tire tested in the red trace allowed for a steeper deceleration curve, meaning the car slowed at a greater rate.
Heat is quick and easy to produce, but it does mean we have to then deal with the excess thermal energy in and around the brakes before the materials become thermally overloaded. That’s a discussion for a different day, but you get the basic principles we’re working within.
Now, a very similar relationship is taking place at your four relatively tiny contact patches. Friction between the tire and the road produces heat that transfers the kinetic energy out of the car, but many more complex operations are happening, too.
A tire’s relationship with the road plays out on a nearly microscopic level. Elastic deformation within the tread surface pulls and stretches the rubber to make more complete contact with the pavement’s countless tiny surface features. Every bit of deformation creates interference between the two that allows the tire to grip the road.
Very generally speaking, that’s why a softer tire has more grip than a harder tire: The softer rubber deforms more at that miniscule level, allowing it to better squirm into the cracks, bumps, ripples, grains and pockmarks in the road surface.
And ultimately, it’s the tires, not the brakes, that stop the car. They’re the final link in the braking chain. So when it comes to tuning a brake system, don’t shortchange this part of the operation. Everything from age, compound, pressure, camber settings and rate of weight transfer can affect a given tire’s relationship with the road and therefore affect braking performance.
Photography Credit: J.G. Pasterjak
To help preserve solid braking integrity, here are a few tire-focused questions to ask yourself:
- Do the static camber settings preserve enough contact patch that straight-line braking won’t be negatively affected? A tire with a lot of negative camber will have the same contact patch area, but when not in a cornering mode, much of that contact patch can be tread shoulder and not tread itself. This can negatively affect braking.
- Does the amount of dynamic weight transfer experienced under braking pair well with the front-to-rear brake proportioning pressure? When the rear wheels unload under braking, they have less contact patch and, therefore, less grip. Sending a lot of brake pressure to unloaded tires just takes away potential from tires with more load. Proportion tuning is an important part of testing. And remember, when you change spring rates, you might change the amount of pitch the car sees under braking, which could necessitate a proportion adjustment.
- Does the compound of the tires pair well with the friction level of the brakes? Low-friction pads and high-friction tires, or the opposite, can make for tricky brake modulation. Your brake supplier will likely have recommendations for best use with 200tw tires, R-comps, slicks and everything in between.
- Are all four of the tires capable of producing similar grip levels? Are the tires old? Did two of them sit outside for the last six months while the other two remained inside? Did you swap to a single spare that was either fresher or older than the other three? Typically, your brakes are only as good as your single worst tire, so understand that making changes to one corner’s rubber can greatly affect overall stopping performance.
